Field of the Invention
This invention is in the field of telecommunications, in particular wireless telecommunications utilizing novel modulation techniques.
Description of the Related Art
Modern electronics communications, such as optical fiber communications, electronic wire or cable based communications, and wireless communications all operate by modulating signals and sending these signals over their respective optical fiber, wire/cable, or wireless mediums or communications channels. In the case of optical fiber and wire/cable, often these data communications channels consist of one (or between one and two) dimensions of space and one dimension of time. In the case of wireless communications, often these communications channels will consist of three dimensions of space and one dimension of time. However, for many ground-based wireless applications, often the third spatial dimension of height or altitude is less important than the other two spatial dimensions.
As they travel through the communications channel, the various signals, which generally travel at or near the speed of light, are generally subject to various types of degradation or channel impairments. For example, echo signals can potentially be generated by optical fiber or wire/cable medium whenever a signal encounters junctions in the optical fiber or wire/cable. Echo signals can also potentially be generated when wireless signals bounce off of wireless reflecting surfaces, such as the sides of buildings, and other structures. Similarly frequency shifts can occur when the optical fiber or wire/cable pass through different regions of fiber or cable with somewhat different signal propagating properties or different ambient temperatures. For wireless signals, signals transmitted to or from a moving reflector, or to or from a moving vehicle are subject to Doppler shifts that also result in frequency shifts. Additionally, the underlying equipment (i.e. transmitters and receivers) themselves do not always operate perfectly, and can produce frequency shifts as well.
These echo effects and frequency shifts are unwanted, and if such shifts become too large, can result in lower rates of signal transmission, as well as higher error rates. Thus methods to reduce such echo effects and frequency shifts are of high utility in the communications field.
In previous work, exemplified by applicant's U.S. patent applications U.S. 61/349,619, U.S. Ser. No. 13/177,119, U.S. Ser. No. 13/430,690 and as well as U.S. Pat. No. 8,547,988, applicant taught a novel method of wireless signal modulation that operated by spreading data symbols over a larger range of times, frequencies, and spectral shapes (waveforms) than was previously employed by prior art methods (e.g. greater than such methods as Time Division Multiple Access (TDMA), Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency-Division Multiplexing (OFDM), or other methods).
Applicant's methods, previously termed “Orthonormal Time-Frequency Shifting and Spectral Shaping (OTFSSS)” in U.S. Ser. No. 13/117,119 (and subsequently referred to by the simpler “OTFS” abbreviation in later patent applications such as U.S. Ser. No. 13/430,690) operated by sending data in larger “chunks” or frames than previous methods. That is, while a prior art CDMA or OFDM method might encode and send units or frames of “N” symbols over a communications link over a set interval of time, applicant's OTFS methods would typically be based on a minimum unit or frame of N2 symbols, or N×M symbols, and often transmit these N2 symbols or N×M symbols over longer periods of time. In some embodiments, these data symbols may be complex numbers.
According to this type of scheme, each data symbol from the N2 symbol or N×M symbols would typically be distributed, in a lossless and invertible (e.g. reversible) manner, across a plurality of distinguishable (e.g. usually mutually orthogonal) waveforms over a plurality of different times and plurality of different frequencies. These different times and frequencies were generally chosen according to the time delay and Doppler-shift channel response parameters of the wireless channel. Due to this lossless spreading, and selection of different times and frequencies, the information from each data symbol was spread throughout the plurality of different times and different frequencies, so that all data symbols in the frame were equally impacted by the time delay and Doppler frequency shift characteristics of the channel. These methods helped made the communications channel more “stationary” (e.g. deterministic and non-fading) as a result. That is, within a given frame, there were no data symbols subject to greater distortion or fading, relative to other data symbols.
In some OTFS modulation embodiments, each data symbol or element that is transmitted was also spread out to a much greater extent in time, frequency, and spectral shape space than was the case for prior art methods. As a result, at the receiver end, it often took longer to start to resolve the value of any given data symbol because this symbol had to be gradually built-up or accumulated as the full frame of N2 symbols is received.
Thus some embodiments of applicant's prior work taught a wireless communication method that used a combination of time, frequency and spectral shaping to transmit data in convolution unit matrices (data frames) of N·N (N2) (e.g. N×N, N times N) symbols. In some embodiments, either all N2 data symbols are received over N spreading time intervals (each composed of N time slices), or none are. In other embodiments this requirement was relaxed.
To determine the times, waveforms, and data symbol distribution for the transmission process, the N2 sized data frame matrix could, for example, be multiplied by a first N·N time-frequency shifting matrix, permuted, and then multiplied by a second N·N spectral shaping matrix, thereby mixing each data symbol across the entire resulting N·N matrix. This resulting data matrix was then selected, modulated, and transmitted, on a one element per time slice basis. At the receiver, the replica matrix was reconstructed and deconvoluted, revealing a copy of the originally transmitted data.
For example, in some embodiments taught by U.S. patent application Ser. No. 13/117,119, the OTFS waveforms could be transmitted and received on one frame of data ([D]) at a time basis over a communications link, typically processor and software driven wireless transmitter and receiver. All of the following steps were usually done automatically using at least one processor.
This first approach used frames of data that would typically comprise a matrix of up to N2 data elements, N being greater than 1. This method was based on creating an orthonormal matrix set comprising a first N×N matrix ([U1]) and a second N×N matrix ([U2]). The communications link and orthonormal matrix set were typically chosen to be capable of transmitting at least N elements from a matrix product of the first N×N matrix ([U1]), a frame of data ([D]), and the second N×N matrix ([U2]) over one time spreading interval (e.g. one burst). Here each time spreading interval could consist of at least N time slices. The method typically operated by forming a first matrix product of the first N×N matrix ([U1]), and the frame of data ([D]), and then permuting the first matrix product by an invertible permutation operation P, resulting in a permuted first matrix product P([U1][D]). The method then formed a second matrix product of this permuted first matrix product P([U1][D]) and the second N×N matrix ([U2]) forming a convoluted data matrix, according to the method, this convoluted data matrix could be transmitted and received over the wireless communications link by:
On the transmitter side, for each single time-spreading interval (e.g. burst time), the method operated by selecting N different elements of the convoluted data matrix, and over different said time slices in this time spreading interval, using a processor to select one element from the N different elements of the convoluted data matrix, modulating this element, and wirelessly transmitting this element so that each element occupies its own time slice.
On the receiver side, the receiver would receive these N different elements of the convoluted data matrix over different time slices in the various time spreading intervals (burst times), and demodulate the N different elements of this convoluted data matrix. These steps would be repeated up to a total of N times, thereby reassembling a replica of the convoluted data matrix to the receiver.
The receiver would then use the first N×N matrix ([U1]) and the second N×N matrix ([U2]) to reconstruct the original frame of data ([D]) from the convoluted data matrix. In some embodiments of this method, an arbitrary data element of an arbitrary frame of data ([D]) could not be guaranteed to be reconstructed with full accuracy until the convoluted data matrix had been completely recovered.
U.S. patent application Ser. No. 13/117,119 and its provisional application 61/359,619 also taught an alternative approach of transmitting and receiving at least one frame of data ([D]) over a wireless communications link, where again this frame of data generally comprised a matrix of up to N2 data elements (N being greater than 1). This alternative method worked by convoluting the data elements of the frame of data ([D]) so that the value of each data element, when transmitted, would be spread over a plurality of wireless waveforms, where each individual waveform in this plurality of wireless waveforms would have a characteristic frequency, and each individual waveform in this plurality of wireless waveforms would carry the convoluted results from a plurality of these data elements from the data frame. According to the method, the transmitter automatically transmitted the convoluted results by shifting the frequency of this plurality of wireless waveforms over a plurality of time intervals so that the value of each data element would be transmitted as a plurality of frequency shifted wireless waveforms sent over a plurality of time intervals. At the receiver side, a receiver would receive and use a processor to deconvolute this plurality of frequency shifted wireless waveforms sent over a plurality of times, and thus reconstruct a replica of at least one originally transmitted frame of data ([D]). Here again, in some embodiments, the convolution and deconvolution schemes could be selected so such that an arbitrary data element of an arbitrary frame of data ([D]) could not be guaranteed to be reconstructed with full accuracy until substantially all of the plurality of frequency shifted wireless waveforms had been transmitted and received. Between frames, the same patterns of time shifts and frequency shifts may repeat, so between frames, these time shifts and frequency shifts can be viewed as being cyclic time sifts and cyclic frequency shifts.
Within a given frame, however, although the time shifts and frequency shifts may in some embodiments also be cyclic time shifts and cyclic frequency shifts, this need not always be the case. For example, consider the case where the system is transmitting an M×N frame of data using M frequencies, over N time periods. Here for each time period, the system may simultaneously transmit M OTFS symbols using M mutually orthogonal carrier frequencies (e.g. tones, subcarriers, narrow band subcarriers, OFDM subcarriers, and the like). The OFTS carrier frequencies (tones, subcarriers) are all mutually orthogonal, and considering the N time periods, are also reused each time period, but need not be cyclic.
In other embodiments, the methods previously disclosed in US patent application Ser. Nos. 13/927,091; 13/927/086; 13/927,095; 13/927,089; 13/927,092; 13/927,087; 13/927,088; 13/927,091; and/or provisional application 61/664,020 may be used for some of the OTFS modulation methods disclosed herein. The entire contents of US patent application Ser. Nos. 13/927,091; 13/927/086; 13/927,095; 13/927,089; 13/927,092; 13/927,087; 13/927,088; 13/927,091; 14/583,911; 62/027,213 and 61/664,020 are incorporated herein by reference in their entirety.